There are many procedures associated with the oral cavity in which a precise three-dimensional representation of the cavity is very useful to the dental practitioner.
Such representations enable the practitioner to study the cavity of individual patients in a similar manner to the study of the traditional plaster model. More importantly, three-dimensional numerical entities of the dental cavity also allow the practitioner to study methods or approaches when dealing with particular dental problems of any given patient, and for the design of physical entities in relation therewith. For example, in prosthodontics, a computer model of a patient's teeth may be manipulated to provide machining data to manufacture a physical model of the intra oral cavity, and/or to design and manufacture a coping and/or a prosthesis.
A parameter used in the design and manufacture of a dental prosthesis, such as a crown or bridge, is the finish line, or transition boundary between the prosthesis and the dental preparation, and this needs to be precisely defined in three-dimensions. Obtaining the finish line coordinates from a computer virtual model is more efficient and often more accurate than from a plaster cast, and moreover facilitates the production of such a prosthesis, for example via CNC machining, rapid prototyping, or other computerised technologies, if desired.
However, it is often the case that when scanning the intra oral cavity to obtain 3D data of the preparation and finish line on which the virtual model is based, part of the finish line, and possibly also the shoulder and other parts of the preparation, may be obscured by soft tissues such as the gum that, no longer being pushed by the dental surfaces that have been removed, deform to cover at least a part of the finish line on the prepared dental site.
Additionally or alternatively, part or all of the finish line may be obscured by other agents, including, for example, accumulation of one or more of saliva, blood, lubricant used with a dental drill, debris resulting from working the dental site, and so on.